linux-kernel - Re: [PATCH v6 3/9] rust: sync: atomic: Add ordering annotation types

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Message-ID: <aG_RcB0tcdnkE_v4@Mac.home>
Date: Thu, 10 Jul 2025 07:42:56 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Andreas Hindborg <a.hindborg@...nel.org>
Cc: Benno Lossin <lossin@...nel.org>, linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org, lkmm@...ts.linux.dev,
	linux-arch@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
	Alex Gaynor <alex.gaynor@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
	Danilo Krummrich <dakr@...nel.org>, Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mark Rutland <mark.rutland@....com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Lyude Paul <lyude@...hat.com>, Ingo Molnar <mingo@...nel.org>,
	Mitchell Levy <levymitchell0@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH v6 3/9] rust: sync: atomic: Add ordering annotation types

On Thu, Jul 10, 2025 at 02:00:59PM +0200, Andreas Hindborg wrote:
> "Benno Lossin" <lossin@...nel.org> writes:
> 
> > On Thu Jul 10, 2025 at 8:00 AM CEST, Boqun Feng wrote:
> >> Preparation for atomic primitives. Instead of a suffix like _acquire, a
> >> method parameter along with the corresponding generic parameter will be
> >> used to specify the ordering of an atomic operations. For example,
> >> atomic load() can be defined as:
> >>
> >> 	impl<T: ...> Atomic<T> {
> >> 	    pub fn load<O: AcquireOrRelaxed>(&self, _o: O) -> T { ... }
> >> 	}
> >>
> >> and acquire users would do:
> >>
> >> 	let r = x.load(Acquire);
> >>
> >> relaxed users:
> >>
> >> 	let r = x.load(Relaxed);
> >>
> >> doing the following:
> >>
> >> 	let r = x.load(Release);
> >>
> >> will cause a compiler error.
> >>
> >> Compared to suffixes, it's easier to tell what ordering variants an
> >> operation has, and it also make it easier to unify the implementation of
> >> all ordering variants in one method via generic. The `TYPE` associate
> >> const is for generic function to pick up the particular implementation
> >> specified by an ordering annotation.
> >>
> >> Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
> >> Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> >
> > One naming comment below, with that fixed:
> >
> > Reviewed-by: Benno Lossin <lossin@...nel.org>
> >
> >> ---
> >>  rust/kernel/sync/atomic.rs          |  3 +
> >>  rust/kernel/sync/atomic/ordering.rs | 97 +++++++++++++++++++++++++++++
> >>  2 files changed, 100 insertions(+)
> >>  create mode 100644 rust/kernel/sync/atomic/ordering.rs
> >
> >> +/// The trait bound for annotating operations that support any ordering.
> >> +pub trait Any: internal::Sealed {
> >
> > I don't like the name `Any`, how about `AnyOrdering`? Otherwise we
> > should require people to write `ordering::Any` because otherwise it's
> > pretty confusing.
> 
> I agree with this observation.
> 

I'm OK to do the change, but let me show my arguments ;-)

* First, we are using a language that supports namespaces,
  so I feel it's a bit unnecessary to use a different name just because
  it conflicts with `core::any::Any`. Doing so kinda undermines the
  namespace concepts. And we may have other `Any`s in the future, are we
  sure at the moment we should keyword `Any`?

* Another thing is that this trait won't be used very often outside
  definition of functions that having ordering variants, currently the
  only users are all inside atomic/generic.rs.

I probably choose the `ordering::Any` approach if you guys insist.

Regards,
Boqun

> 
> Best regards,
> Andreas Hindborg
> 
> 
>